Abstract
Purpose: :
Dry eye (DE) has been divided into two different categories, evaporative and tear production-deficiency. During blinking, meibomian glands secrete lipids onto the preocular tear film. Changes in quantity or quality of the meibomian lipids affect the evaporation of the aqueous layer. This study was conducted to evaluate the effect of excess meibum in reducing the evaporation rate over time in patients with and without dry eye.
Methods: :
The effect of digital expression of meibomian glands on aqueous tear evaporation rate was tested in 11 normal subjects and 16 DE patients. DE group was divided into two groups based on clinical examination. Classic Keratoconjunctivitis Sicca (KCS) group with clear and easily expressed meibomian gland secretion and KCS with meibomian gland dysfunction (MGD) group with turbid and difficult to expressed meibomian gland secretion. Evaporative measurements were performed at baseline and following digital expression of both upper and lower lid meibomian glands. Each measurement took 10 minutes to complete and 2 minutes were allowed between measurements. A total of four sequential measurements were taken at 12, 24, 36 and 48 minutes following digital expression. An evaporometer (Oxdata, Portland, Oregon, USA) was used at two ranges of relative humidity (RH) 25% to 35% and 35% to 45%.The data was expressed in µl/cm2/min.
Results: :
An increase in evaporation rate of the tear film was noted in all measurements using both RH in the classic KCS, and KCS with MGD groups compared to normals (p<0.05). The average evaporation rate at RH 25-35% and 35-45% was 0.056±0.016 and 0.040±0.008 for the classic KCS group; 0.055±0.026 and 0.037±0.019 for KCS with MGD; 0.033±0.012 and 0.023±0.008 for the normal group, respectively. In addition, a statistically significant decrease in evaporation rate was present in the normal and KCS with MGD groups between baseline and the first measurement following digital expression for both RH (p<0.05). There was no statistically significant difference between baseline and the other three measurements (p>0.05). The classic KCS group did not show a statistically significant change at any measurement following digital expression compared to baseline (p>0.05).
Conclusions: :
The Classic KCS and KCS with MGD patients showed an increase in tear evaporation rate compared to the normal group. The aqueous tear evaporation diminished in the normal and KCS with MGD groups following digital expression of the meibomian glands. Yet, this positive effect was transient and almost negligible after the second measurement.
Keywords: cornea: tears/tear film/dry eye • cornea: tears/tear film/dry eye • lipids